You are what you eat — and that maxim may include the shape and geometry of your jawbone.
A lifetime of strenuous mastication on muktuk and tough wild meat harvested near the Chukchi Sea gave a group of pre-contact Inupiat Alaskans rounder and tougher jawbones, a finding that may offer physical anthropologists another method to sort out the dietary habits of other prehistoric peoples, says a research paper published this summer in the American Journal of Physical Anthropology.
It turns out that what people eat, and whether they they used their teeth to prep hides, gradually alters the structure of their mandibles in predictable ways, according to a study that used the X-ray guns and the principles of engineering stress to analyze 63 jawbones from Inupiat people who lived near the modern village of Point Hope 300 to 400 years ago.
Scientists from the Johns Hopkins Center for Functional Anatomy and Evolution compared these Alaskan remains to the jawbones from 42 Arikara Indians who lived in what is now South Dakota about the same time. They found dramatic differences that could be traced back to known differences in diet and lifestyle of the two groups.
"Genetics creates a blueprint of the bone, but a lot of things influence the bone's construction," said lead author Megan Holmes, a Johns Hopkins graduate student in this online story about the findings. "Our research aimed to see how much of the mandible's -- or jaw bone's -- shape is plastic, a response to environmental influences, such as diet, and how much is genetic."
Working with Johns Hopkins biological anthropologist Christopher Ruff, Holmes measured specific parts of the jawbones with calipers and X-rays. They examined 52 juvenile and 11 adult remains from Alaska, and 32 juvenile and 10 adult Arikara -- all borrowed from collections (here and here) at the American Museum of Natural History.
Evolving with what we eat
The gravel spit at Point Hope -- known as "Tiagara" or "forefinger" in the Inupiaq language -- is one of the oldest continuously occupied sites in North America, with archaeological artifacts dating back 2,500 years or more. The Arikara remains came from the Sully site in South Dakota.
"Before we can make inferences about what the shape of a bone tells us, like what environment the individual lived in, who it's related to or what it ate, we have to understand what creates that shape," Holmes explained. "The idea that function influences the shape of jaw bones is great for the archeological record in terms of discovering the diet of a population, and it's also really useful for reconstructing the fossil record -- finding which fossils are related to which, and how."
Because scientists already knew a great deal about the diet of these particular pre-contact Native Americans, they could investigate how their different diets -- the "hard" cuisine of the Point Hope people versus the "softer" foods of the Arikara -- showed up in the structure of adult jawbones.
"Tigara specimens represent a circumpolar population which occupied Point Hope, Alaska between 1200 and 1700 A.D.," the authors wrote in the paper. "Archaeological and ethnographic data indicate a diet consisting of dried meats exploited from marine resources such as fish and sea mammals, which would require heavy masticatory loading for consumption. In addition, there is evidence that the Tigara population utilized their dentition as a tool for gripping, stripping, and softening leather."
The Arikara, on the other hand, ate a more varied diet of both plants and animal foods, and simply didn't chew as hard or as much.
"Direct comparisons of dental microwear patterns between these two populations demonstrate their dietary differences, and are consistent with heavier loading (as well as a more abrasive diet) among the Tigara," the authors wrote.
By comparing the remains of children with those from adults, Holmes and Ruff found that the changes largely occurred over a lifetime, altering the geometry of the jawbones in predictable ways, the scientists explained.
"In the Point Hope population, for example, they found round, wide jaw bones -- a result of having to exert more force to chew a harder diet," said this story. "The Arikara, on the other hand, did not show this expansion, which they attributed to the lighter chewing requirement of a softer diet."
The conclusion:
"Use over time and not just genetics informs the structure of jaw bones in human populations," the authors explained in this story. "The findings may be used to predict the diet of an ancient population, even if little evidence exists in the fossil record. It can also make it easier for scientists to pinpoint the genetic relationship between fossils."
Contact Doug O'Harra at doug(at)alaskadispatch.com